Fermilab's
Technical Division has completed highly successful tests of
the first superconducting quadrupole assemblies for the US LHC Accelerator
Project. The 19-foot, 12,000-pound magnets, part of an overall $531 million
effort in the U.S., are bound for the Large Hadron Collider under construction
at CERN, the European Particle Physics Laboratory in Geneva, Switzerland.

“The first results have been very good,” said Fermilab LHC project manager
Jim Kerby, of the lab’s Technical Division.“They’ve performed well above
where they need to be for the [LHC operation]. In fact, they’ve performed
better than any magnets we’ve ever made here.”

The LHC superconducting magnets are designed to reach a peak magnetic
field of 9 Tesla; superconducting magnets at Fermilab’s Tevatron reach
4.4 Tesla.

“In terms of production accelerator magnets,” said Fermilab’s Jim Strait,
the US LHC project manager,“this is about as high a field as anyone has
ever achieved. These are some of the best production accelerator magnets
ever made.”

The system is working.

With outstanding performances by these first two assemblies at super-
conducting temperatures, Kerby added,“we know that we do not have
a systematic problem with our production process. That doesn ’t rule out
random problems, but it lets us know that our overall process is working.
It’s a testimony to good quality assurance practices and the dedication of
everyone who has worked on the project.”

The tests have been performed at Fermilab’s Industrial Center, on
quadrupole assemblies destined for the beam interaction points at LHC.
The assemblies incorporate two Fermilab-produced quadrupoles (focusing
magnets) joined with a CERN-designed correction dipole (steering magnet),
with the components stretching about 40 feet.

The assemblies are slid into a vacuum vessel and chilled with superfluid
helium to around 2 kelvins (2 degrees celsius above absolute zero).
Each half of the assembly is tested individually. The magnets are “trained ”
with electric current flowing through them until they quench, or rise above
superconducting temperatures. When the magnets quench, they “remember ”
the levels of current flow they’ve experienced, and the intensity of the
magnetic field they have generated. If all goes
well, they will equal or surpass those standards in
succeeding thermal cycles, until they have reached
their performance goals.

For their role in the LHC, the magnets are
expected to generate a magnetic field gradient of
205 Tesla per meter, with some portions requiring
214 T/m. Fermilab is expected to train the magnets
up to 230 T/m, providing a high level of confidence
for their performance under the most stringent
experimental conditions in the collider.

When tested in 2001, the Fermilab prototype
quenched at an electrical current just under
12,000 amperes. The first half of the first
production assembly went all the way to 13,000
amperes without quenching, reaching a field
gradient of 233 T/m in the first thermal cycle.
The second magnet reached 12,710 amperes,
producing a gradient of 229 T/m on its first quench,
then hit 12,955 amperes and 232 T/m on the second
quench — again, above the target of 230 T/m.

“If I could bottle this kind of result, I would,”
Kerby said.

While production and testing continue on the
remainder of the 18 Fermilab magnets, another
production process is beginning. The Fermilab
team will receive 18 LHC magnets produced at
KEK in Japan. At Fermilab, they will be assembled
into their cryostat structures before being shipped
to CERN.

Brookhaven and Lawrence Berkeley National
Laboratories round out the U.S. collaboration on
LHC accelerator components. Brookhaven has built
and tested beam separator dipole magnets to be
used in specialty regions around the 27-kilometer
(17-mile)LHC ring. Of an allotment of 20 magnets
of four different types, Brookhaven has completed
13, tested eight, and shipped one to CERN.
Brookhaven is also testing superconducting cable
produced in Europe. Berkeley is working with
Fermilab on superconducting cable; producing
absorbers to protect magnet components from
low-angle debris in the collision region, and
building feed boxes to provide utilities for the
magnets — power, cryogens, vacuum and
instrumentation.

Fermilab was a pioneer in superconducting
accelerator magnets, with more than 1,000
incorporated into the Tevatron, which was
completed in 1983. The US LHC effort means
superconducting magnet production has returned
to Fermilab in a big way.

“We have developed the engineering, scientific
and technical staff to produce the highest-
performing magnets in the world,” Strait said.
“With this project, we have maintained and
extended our leadership in superconducting
magnet technology.”